The present invention relates generally to a fuel feeder for a boiler-type furnace and more particularly to a novel speed control drive unit for a chain-type coal feeder for feeding coal into the furnace.
Chain-type feeder units have been used for many years for feeding particulate fuel such as coal to furnaces and operate in such a way as to deliver a uniform sheet of coal onto a rotor which scatters and throws the coal a predetermined distance into the combustion chamber of the furnace. Normally, a number of these feeders are arranged side-by-side across the width of the furnace. One such feeder is shown in U.S. Pat. No. 2,099,618.
Typically, the feeder unit includes a cast iron housing which attaches to a wall of the furnace adjacent a charge opening and houses a chain bar conveyor that feeds coal onto a rotor which throws the coal through the opening into the furnace. The conveyor is driven by a power take-off from the rotor through a variable speed drive mechanism which enables the speed of the conveyor to be adjusted as necessary to deliver selected amounts of fuel to the rotor to compensate for variations in the size, density, and moisture content of the fuel. In the known conventional feeders, the drive transfer components connecting the rotor to the chain conveyor are usually contained in a totally enclosed cast iron casing mounted integrally with one sidewall of the housing where they are exposed to the heat from the sidewall and the furnace. The drive transfer assembly includes many individual customized parts such as gears, lever arms, ratchet and pall mechanisms, clutch mechanisms, etc., all of which are run in an oil bath in the casing in an attempt to maintain the components at a relatively low temperature. While this type of design initially functions fairly well to provide a variable speed drive connection between the rotor and the chain conveyor, problems arise because of the heat buildup within the closed casing. For example, the oil experiences thermal breakdown and the bearings and seals within the drive transfer unit often fail prematurely. In addition, clutch plates become soaked with oil and slip prematurely which cause the chain feeder to interrupt or even stop feeding fuel to the rotor.
Such conventional drive units are not dependable, are difficult and expensive to maintain and have short life, and the feeder units experience substantial downtime. The components are not readily accessible and maintenance personnel consider it a nightmare when attempting to repair the drive transfer unit. In addition, the casing requires substantial machining and thus adds significantly to the cost of the overall housing for the feeder unit.